Capacitive Touch Charge Transfer Lateral Mode Technology 3

Despite its extremely low power consumption, the lateral mode sensor can easily penetrate several millimeters thick plastic, glass, and other materials, detecting the use of multi finger touch. The electrodes can be made of any conductive material, such as ITO, and can be of almost any size and shape. The noise cancellation algorithm can help these sensors eliminate the noise generated by modules such as LCD, usually without the need for a separate shielding layer, thereby improving the optical transmission performance of the display, while reducing the construction cost and backlight power requirements of the product. The QMatrix lateral mode circuit introduced by the manufacturer adopts a dual slope conversion form, which ensures high stability of the circuit to changes in time and temperature (Figure 4).  diode

Figure 4: Schematic diagram of QMatrix lateral mode circuit

The chips developed by manufacturers collect signals coupled to the receiving electrode through sampling capacitors synchronized with the driving pulse switch, and improve the signal-to-noise ratio using a pulse train. The number of pulses in each pulse train directly affects the gain of the circuit, making it easy to adjust the circuit gain to suit different panel materials, button sizes, and panel thicknesses.

The first ramp generated by the pulse train is a stepped waveform signal applied to the sampling capacitor. After the pulse train, the driver switches the reference terminal of the slope resistor to a high level, discharges the sampling capacitor until the charge is exhausted, and the voltage comparator detects the zero crossing point. The ramp time required to obtain the zero crossing point is proportional to the coupling of X and Y charges, and decreases with the user's finger touching the panel surface (Figure 5). diode